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 Previous: The K7RA Solar Update |  Next: FCC Issues First Waiver for Government-Sponsored Disaster Drill |
H. Ward Silver, N0AX
ARRL Contributing Editor
n0ax@arrl.org
October 27, 2009
Solar cells -- can't top 'em. Ultracapacitors -- can't top 'em. They produce an unstoppable electromotive force! Powering everything from power amplifiers to personal phones, no other practical product packs the punch of electrochemical cells, the first true electrical device. Ubiquitous though they may be, our knowledge of their inner workings is often weak. Discharge your memory banks into this quiz to see how you measure up!
1) What causes the terminal voltage of a battery to drop under load?
a. ennui
b. internal resistance
c. contact delamination
d. electromigration
2) Who invented the first electrochemical cell?
a. Volta
b. Voltaire
c. Volare
d. Voldemort
3) What's the difference between a battery and a cell?
a. Cells are only found in laboratories.
b. There's no difference -- the terms mean the same thing.
c. Batteries have more current capacity.
d. Batteries are made up of more than one cell.
4) Volume being equal, which type of battery will deliver the most energy?
a. Lead-acid
b. Zinc-air
c. Lithium-ion
d. Carbon-zinc
5) Which type of charger maintains a battery at a stable voltage?
a. Constant current
b. Trickle
c. Float
d. Training
6) Which type of battery can be recharged?
a. Primary
b. Secondary
c. Tertiary
d. Stationary
7) What does "MH" stand for in the battery type abbreviation "NiMH"?
a. Metallic Hydrogen
b. Maximum Horsepower
c. Metal Hydride
d. Mega Henries
8) What is necessary for a battery to produce the flow of electrons?
a. A completed external circuit.
b. A liquid or gel electrolyte.
c. Free metallic cations.
d. An acid and a base, separated by a dielectric.
9) A deep-cycle battery is specially designed so that it can be used in what way?
a. Supplying pulses of high current.
b. To maintain a constant output voltage with wide variations of current.
c. Underwater applications, such as sonar and remote vehicle propulsion systems.
d. Be repeatedly discharged to low output voltage between charges.
10) If a battery is a "pull-out," what does that mean?
a) It slides in and out of a battery holder.
b) It has been removed from some other piece of equipment.
c) It failed to meet manufacturer specifications and is sold at a discount.
d) These are new batteries, just received from the manufacturer.
Bonus: Ampere-hours (Ah) have units of coulombs -- an amount of charge. What assumption allows Ah to be used as a measure of deliverable energy instead?
Answers
1. b -- Current flowing through the internal resistance causes a voltage drop, just like a separate resistor.
2. a -- He was rewarded (eventually) by having the unit of electromotive force -- the volt -- named after him.
3. d -- For example, a 9 V battery consists of six 1.5 V cells in series. That's why we buy "D cells" and not "D batteries."
4. c -- This is the reigning energy density champ of consumer batteries, but new "chemistries" are being devised all the time!
5. c -- Float charging applies a constant voltage to the battery after full-charge is reached.
6. b -- Although it helps for the battery to be stationary, only secondary batteries can be recharged.
7. c -- Some metallic hydrides (compounds of metal and hydrogen) can store and release electrons quite effectively.
8. a -- Without a path for the electrons, the chemicals in the cell cannot react by exchanging electrons.
9. d -- A regular automotive battery used in this way quickly loses its energy storage capacity. Batteries with a large reserve capacity (RC) are the right ones to use.
10. b -- Rechargeable batteries are often removed from service on a fixed schedule to ensure that equipment operates properly. They may have significant service life left, but generally less than that guaranteed by the manufacturer. Caveat emptor!
Bonus -- The assumption is that the battery maintains a constant output voltage. The units of voltage are joules ÷ coulombs, so Ah × V = joules (or energy).
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